The present invention relates to a system for controlling the fuel injection of an automotive engine in dependency on pressure and temperature in cylinders of the engine. The pressure in the cylinders is used as a parameter representing quantity of intake air, for deciding air-fuel ratio of mixture.
Recently, there has been proposed a system for accurately controlling the ignition timing and the air-fuel ratio by detecting combustion pressure in each cylinder of the engine with a pressure sensor. Japanese Patent Application Laid-Open No. 60-47836 discloses a system for controlling the air-fuel ratio based on pressure in cylinders. In the system, a fuel injection pulse width is derived from a basic fuel injection pulse width table in accordance with detected pressure and engine speed.
However, the pressure in the cylinder is closely related with temperature in a combustion chamber. The temperature changes in accordance with temperature of the wall of the combustion chamber, which changes with coolant temperature, and ambient temperature. Accordingly, it is difficult to estimate the air quantity in dependency only on pressure in the cylinder. Further, in a multiple cylinder engine, the temperature of the wall of the combustion chamber differs at every cylinder due to the disposition of a coolant passage. Consequently, in the fuel injection control system, the air-fuel ratios in cylinders are different. As a result, combustion of the fuel becomes unstable, causing aggravation of fuel consumption and emission control.
On the other hand, the intake air quantity in each cylinder cannot be measured with a conventional air-flow meter. Accordingly, the air-fuel ratio for each cylinder cannot be controlled by the system employing the air-flow meter. In addition, the air-flow meter becomes a resistance to air, resulting in reduction of intake efficiency.